Inlet air control method for a vehicle HVAC system having an air quality sensor

ABSTRACT

An improved HVAC control method immediately closes an air inlet valve to provide full cabin air recirculation when an outside air quality sensor detects polluted air, and thereafter progressively re-opens the air inlet valve at a determined rate when the air quality sensor detects unpolluted air. Preferably, the air quality sensor quantifies the pollution level of the outside air, and the opening rate of the air inlet valve is determined based on the detected pollution level. Following a high level of detected air pollution, the valve is re-opened at a relatively slow rate, and following a low level of detected air pollution, the valve is re-opened at a relatively fast rate.

TECHNICAL FIELD

This invention relates to a vehicle heating, ventilation and airconditioning (HVAC) system having an air quality sensor and an inlet aircontrol valve, and more particularly to an improved method of operatingthe inlet air control valve.

BACKGROUND OF THE INVENTION

Vehicle HVAC systems commonly include an inlet air controller such as amovable valve or shutter (referred to herein simply as an inlet airvalve) that is positioned to control what proportion of the inlet air isdrawn from inside and outside the vehicle cabin. In a typicalapplication, a system controller positions the air inlet valve tooptimize system efficiency and occupant comfort, and the occupant ispermitted to override the normal control when full cabin airrecirculation or full outside air is desired. For example, cabin airrecirculation may be used to limit the intrusion of polluted air whendriving in congested traffic, and full outside air may be used to purgethe cabin of smoke or odors. However, the average driver frequentlyfails to manually position the inlet air valve as recommended, andsometimes polluted air has already entered the cabin by the time thedriver switches to cabin air recirculation. For these reasons, the trendis to equip vehicle HVAC systems with a filtering system and one or moreair quality sensors; the filtering system filters particulates and odorsfrom the inlet air, and the inlet air valve is automatically positionedbased on the air quality sensor to minimize the amount of polluted airentering the inlet air stream. See, for example, the U.S. Pat. No.5,725,425 to Rump et al., issued on Mar. 10, 1998, and incorporated byreference herein.

A problem that occurs with automated positioning of the inlet air valvebased on air quality sensing is that the HVAC system can be repeatedlycycled between the outside air and recirculation modes, particularlywhen the vehicle is operated in congested city traffic. Each opening andclosing of the air inlet valve changes the HVAC noise level in thecabin, and the changing noise level can be annoying to the vehicleoccupants. Accordingly, what is needed is an improved method ofoperating the air inlet valve in response to detected inlet air qualitythat provides the improved cabin air quality in a way that is lessperceptible to the vehicle occupants.

SUMMARY OF THE INVENTION

The present invention is directed to an improved method for controllingan inlet air valve in a vehicle HVAC system including an air qualitysensor in an outside air inlet passage, wherein the air inlet valve isimmediately closed to provide cabin air recirculation when the sensordetects the presence of polluted air, and is thereafter re-opened at adetermined rate when the outside air is no longer polluted. In apreferred embodiment, the air quality sensor output quantifies thepollution level of the inlet air, and the opening rate of the air inletvalve is determined based on the detected level. Following a high levelof detected air pollution, the valve is re-opened at a relatively slowrate, and following a low level of detected air pollution, the valve isre-opened at a relatively fast rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicle HVAC system according to thisinvention, including an air inlet valve, an air quality sensor and amicroprocessor-based control unit.

FIG. 2, Graphs A-C, depict the operation of the system of FIG. 1 in aperiod of driving in congested traffic. Graph A depicts the output ofthe air quality sensor, Graph B depicts a conventional control of theair inlet valve, and Graph C depicts a control of the air inlet valveaccording to this invention.

FIG. 3, Graphs A-C, depict the control of the air inlet valve accordingto this invention. Graphs A, B and C respectively depict re-opening ofthe inlet air valve following periods of high, medium and low airpollution levels.

FIG. 4 is a state diagram depicting the functionality of a softwareroutine executed by the microprocessor-based control unit of FIG. 1 incarrying out the control of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the reference numeral 10 generally designates avehicle HVAC system, including a refrigerant compressor 12 coupled to adrive pulley 14 via an electrically activated clutch 16. In theillustrated embodiment, the compressor 12 has a fixed stroke, and thecooling capacity is controlled by cycling the clutch 16. However, itshould be understood that the compressor 12 may alternatively be avariable capacity compressor, in which case an electric or pneumaticstroke control valve is used to achieve capacity control. In any case,the drive pulley 14 is coupled to a rotary shaft of the vehicle engine(not shown) via drive belt 18.

The system 10 further includes a condenser 20, an orifice tube 22, anevaporator 24, and an accumulator/dehydrator 26 arranged in orderbetween the compressor discharge port 28 and suction port 30. A coolingfan 32, operated by an electric drive motor 34, is controlled to providesupplemental air flow through the condenser 20 for removing heat fromcondenser 20. The orifice tube 22 allows the cooled high pressurerefrigerant in line 38 to expand in an isenthalpic process beforepassing through the evaporator 24. The accumulator/dehydrator 26separates low pressure gaseous and liquid refrigerant, directs a gaseousportion to the compressor suction port 30, and acts as a reservoir forthe reserve refrigerant charge. In an alternative system configuration,the orifice tube 22 is replaced with a thermostatic expansion valve(TXV); in this case, the accumulator/dehydrator 26 is omitted, and areceiver/drier (R/D) is inserted in line 38 upstream of the TXV toensure that sub-cooled liquid refrigerant is supplied to the inlet ofthe TXV.

The evaporator 24 is formed as an array of finned refrigerant conductingtubes, and an air intake duct 40 disposed on one side of evaporator 24houses an air filter 41 and an inlet air blower 42 driven by an electricblower motor 43 to force the inlet air past the filter 41 and evaporator24. The air intake duct 40 is bifurcated upstream of the filter 41 andblower 42, and an inlet air valve 44 is adjustable as shown by the servomotor (SM) 46 to control inlet air mixing. Depending on the position ofinlet air valve 44, outside air may enter air intake duct 40 throughduct leg 44 a as indicated by arrow 48, and passenger compartment airmay enter air intake duct 40 through duct leg 44 b as indicated by arrow50. For purposes of this disclosure, the air inlet valve 44 isconsidered to be closed when the leg 44 a is fully restricted, and theinlet air consists essentially of cabin air from the leg 44 b;conversely, the air inlet valve 44 is considered to be open when the leg44 b is fully restricted, and the inlet air consists essentially ofoutside air from the leg 44 a.

An air outlet duct 52 disposed on the downstream side of blower 42 andevaporator 24 houses a heater core 54 formed as an array of finned tubesthat conduct engine coolant. The heater core 54 effectively bifurcatesthe outlet duct 52, and a re-heat valve 56 is adjustable as shown tocontrol how much of the air must pass through the heater core 54. Theheated and un-heated air portions are mixed in a plenum portion 62 ofoutlet duct 52 downstream of re-heat valve 56, and a pair of modecontrol valves 64, 66 direct the mixed air through one or more outlets,including a defrost outlet 68, a panel outlet 70, and a heater outlet72. The mode control valve 64 is adjustable as shown to switch theoutlet air between the defrost and panel outlets 68, 70, and the modecontrol valve 66 is adjustable as shown to control airflow through theheater outlet 72.

The system 10 is controlled by the microprocessor-based control unit 90based on various inputs. In the illustrated embodiment, such inputsinclude: cabin air temperature CAT, the outside air temperature OAT,outside air quality level OAQL, and the usual operator demand inputs,such as the desired temperature, and override controls for the inlet airvalve 44. The CAT and OAT signals are obtained with conventionaltemperature sensors (not shown), and the OAQL signal is provided by theair quality sensor 92. The air quality sensor 92 is mounted on theoutside air inlet leg 44 a as indicated, and its OAQL output signal online 94 provides an indication of the level of pollutants in the inletleg 44 a. In the illustrated embodiment, the sensor 92 may be a ParagonMK IV air quality sensor, available from Paragon AG, in which case theoutput OAQL assumes one of four possible voltage levels following aninitial warm-up period: a first voltage level for clean (i.e.,unpolluted) air, and second, third and fourth levels for increasinglypolluted air. See, for example, the trace of Graph A, FIG. 2, whichrepresents a typical OAQL signal vs. time during driving in congestedtraffic; in Graph A, the level C designates clean air, and the levels I,II and III designate increasingly polluted air.

In response to the above mentioned and other inputs, the control unit 90develops output signals for controlling the compressor clutch 16, thecooling blower motor 34, the blower motor 43, and the air control valves44, 56, 64 and 66. In FIG. 1, the output signal CL for the clutch 16appears on line 96, and the output signal FC for the condenser fancontrol appears on line 98. The output signal IAV for positioning theinlet air valve 44 appears on line 99, and is applied as an input to theservo motor 46, which in turn, is mechanically coupled to inlet airvalve 44 as mentioned above. For simplicity, output signals andactuators for the blower motor 43 and the air control valves 56, 64, 66have been omitted in FIG. 1.

According to the present invention, the control unit 90 regulates theposition of inlet air valve 44 in response to the outside air qualitylevel signal OAQL so as to minimize the admission of polluted air intothe inlet air stream. When the OAQL signal indicates the presence ofpolluted air in inlet leg 44 a, the control unit 90 quickly closes theair inlet valve 46 to provide full cabin air recirculation. When thepolluted air is no longer present, the control unit 90 re-opens theinlet air valve 46 at a determined rate. The re-opening rate isdetermined based on the indicated pollution level prior to theindication of clean air. The different rates for the air quality sensor46 of the illustrated embodiment are graphically depicted in FIG. 3.Each of the Graphs A-C depict an inlet air valve control signal IAVdeveloped by control unit 90 as a function of time. Graph A depicts asituation in which the OAQL signal indicates level I air pollution inthe time interval t0-t1; Graph B depicts a situation in which the OAQLsignal indicates level II air pollution in the interval t0-t1; and GraphC depicts a situation in which the OAQL signal indicates level III airpollution in the interval t0-t1. So long as the OAQL signal indicatesthe presence of polluted air, the inlet air valve 44 is maintainedclosed for full cabin air recirculation (RECIRC) as indicated. When theOAQL signal returns to C (clean air) at time t1, the inlet air valve 44is re-opened (i.e., to full outside air OSA) at a determined rate. Inthe situation depicted by Graph A, the indicated pollution level was low(level I), and the control unit 90 re-opens the inlet air valve 44 at arelatively fast rate A that will fully open the valve 44 at time t2,which may be approximately 12 seconds after time t1. In the situationdepicted by Graph B, the indicated pollution level was medium (levelII), and the control unit 90 re-opens the inlet air valve 44 at a mediumrate B that will fully open the valve 44 at time t3, which may beapproximately 30 seconds after time t1. In the situation depicted byGraph C, the indicated pollution level was high (level III), and thecontrol unit 90 re-opens the inlet air valve 44 at a relatively slowrate C that will fully open the valve 44 at time t4, which may beapproximately 60 seconds after time t1. Alternatively, the rate ofre-opening may be non-linear (exponential, for example) instead oflinear, as designated by the broken traces A′, B′ and C′ in Graphs A, Band C, respectively.

Graphs A and C of FIG. 2 illustrate the effect of the above-describedcontrol (with linear re-opening rates A, B and C) for a period ofdriving in stop-and-go city traffic. The inlet air valve 44 is re-openedat a rate (A, B or C) corresponding to the indicated pollution level (I,II or III) just prior to receipt of the clean air indication. Incontrast, Graph B illustrates a conventional or known control in whichthe air inlet valve 44 is quickly re-opened each time the OAQL signalindicates the presence of clean air. Comparing Graphs B and C, it iseasily seen that the control of the present invention results insignificantly less movement of the inlet air valve 44, and testing hasshown that the cabin noise level fluctuation under such drivingconditions is significantly reduced.

The state diagram of FIG. 4 represents the functionality of a softwareroutine executed by the control unit 90 for carrying out the control ofthis invention. The diagram depicts three states or modes of operation:a Clean Air state 100 in which OAQL=C, a Close Inlet Air Valve state 102that is entered whenever OAQL transitions from C to I, II or III, and aRe-Open Inlet Air Valve state 104 that is entered whenever OAQLtransitions from levels I, II or III to C. In state 100, the controlunit 90 sets the inlet air valve signal IAV at a minimum value MIN forfull outside air (OSA). In state 102, the control unit 90 sets the inletair valve signal IAV at a maximum value MAX for full cabin airrecirculation (RECIRC), and updates a variable OAQL_LAST to store themost recent level of the air quality signal OAQL prior to a transitionto the C level. In state 104, the control unit 90 sets the inlet airvalve signal IAV according to:IAV=MAX−(RATE*T)where RATE is a rate determined as a function of OAQL_LAST, and T is theelapsed time in state 104. Thus, state 104 serves to re-open the inletair valve 44 at a determined rate as described above in respect to FIGS.2-3, and the control unit 90 transitions to the state 106 when IAV hasbeen reduced to the minimum value MIN (for full OSA), provided that OAQLremains at level C. If OAQL transitions from level C to levels I, II orIII while the state 104 is active, the control unit 90 will re-enterstate 102 as indicated in FIG. 4.

In summary, the control of this invention provides a novel andadvantageous way of operating an inlet air valve in response to sensedair quality that achieves the objective of minimizing intrusion ofpolluted air into the vehicle cabin while also minimizing the associatednoise level in the cabin. Since the noise fluctuation introduced by thecontrol is less perceptible to the occupants, the driver is less likelyto override the control in a way that provides less effective filteringof the cabin air. While described in reference to the illustratedembodiment, it is expected that various modifications in addition tothose mentioned above will occur to those skilled in the art. Thus, thecontrol of this invention may be applied to air conditioning systemsconfigured differently than shown in FIG. 1, or to air quality sensorsthat provide an output that is different than described herein. Forinstance, if the air quality sensor 46 is configured to provide anoutput that varies continuously (linear or non-linear) with the detectedlevel of pollution, the re-opening rate may be calibrated as a functionof the sensor output level to achieve essentially the same operation asdepicted in FIGS. 2-3. Accordingly, it will be understood that methodsincorporating these and other modifications may fall within the scope ofthis invention, which is defined by the appended claims.

1. A method of positioning an inlet air valve of a vehicle HVAC systemfor controlling what proportion of inlet air is drawn from outside andinside a vehicle cabin, the system including an air quality sensor fordetecting a pollution level of air outside the vehicle cabin, the methodcomprising the steps of: establishing a first mode of operation forpositioning the inlet air valve to a first position that restricts theinlet air to essentially air from outside the vehicle cabin when the airquality sensor detects unpolluted outside air; establishing a secondmode of operation for positioning the inlet air valve to a secondposition that restricts the inlet air to essentially air from inside thevehicle cabin when the air quality sensor detects polluted outside air;establishing a third mode of operation for moving the inlet air valvefrom the second position to the first position at a determined rate whenthe air quality sensor detects a transition from polluted air tounpolluted air, where the determined rate varies according to apollution level detected during said second mode of operations;transitioning from the third mode of operation to the first mode ofoperation when the air inlet valve reaches said first position and theair quality sensor continues to detect unpolluted air; and transitioningfrom the third mode of operation to the second mode of operation whenthe air quality sensor re-detects polluted air.
 2. (canceled) 3.(canceled)
 4. The method of claim 1, including the steps of: storing thepollution level detected by the air quality sensor during said secondmode of operation; and determining the rate of movement of the air inletvalve during the third mode of operation based on the stored pollutionlevel.
 5. The method of claim 4, including the step of: updating saidstored pollution level during said second mode of operation so that therate of movement of the air inlet valve during the third mode ofoperation is determined based on the detected pollution level just priorto said transition from polluted air to unpolluted air.
 6. The method ofclaim 1, where the determined rate is a linear rate.
 7. The method ofclaim 1, where the determined rate is an exponential rate.